As I've seen before on this game, when there are multiple solutions, the game does not recognize the correctness of the alternative. This means that it is checking against a solution rather than the rules of the game. This is obviously problematic.

Take a look at Columns 2 & 5. Column 5 is filled as OOXXOXOXXO and Column 2 is OOXXOXO-X-. According to the rules, No two rows or columns can have the same sequence. Therefore, Column 2 must end with -OXX. Column 1 then can be completed with -XXO which solves the puzzle.